U.S. patent application number 11/069984 was filed with the patent office on 2005-09-08 for aluminum electrolytic capacitor.
Invention is credited to Hayashi, Kazunari, Honda, Kazumitsu, Nagara, Hisao, Takaoka, Ryoko, Watanabe, Yoshihiro.
Application Number | 20050195557 11/069984 |
Document ID | / |
Family ID | 34879836 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050195557 |
Kind Code |
A1 |
Hayashi, Kazunari ; et
al. |
September 8, 2005 |
ALUMINUM ELECTROLYTIC CAPACITOR
Abstract
An aluminum electrolytic capacitor produced by winding an anode
foil 11 and a cathode foil 12 via a separator 13 impregnated with a
driving electrolyte solution 14, wherein the driving electrolyte
solution 14 comprises a polar solvent, at least one electrolyte
selected from inorganic acids, organic acids, inorganic acid salts,
and organic acid salts, and a random copolymer of polyoxyethylene
and polyoxypropylene having a hydroxy group at one end and a
hydrogen group at the other end and the separator 13 is formed by
overlaying a cellulosic fiber-mixed paper, a cellulosic fiber
paper, and a cotton linter. The present invention provides a
long-lasting driving electrolyte solution higher in electric
conductivity and superior in the chemical self-restoring ability
and heat resistance at high temperature, and an aluminum
electrolytic capacitor using the same.
Inventors: |
Hayashi, Kazunari; (Uji-shi,
JP) ; Takaoka, Ryoko; (Hirakata-shi, JP) ;
Nagara, Hisao; (Uji-shi, JP) ; Honda, Kazumitsu;
(Hirakata-shi, JP) ; Watanabe, Yoshihiro;
(Osaka-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
34879836 |
Appl. No.: |
11/069984 |
Filed: |
March 3, 2005 |
Current U.S.
Class: |
361/504 |
Current CPC
Class: |
H01G 11/52 20130101;
H01G 9/02 20130101; H01G 11/58 20130101; Y02E 60/13 20130101; H01G
9/035 20130101 |
Class at
Publication: |
361/504 |
International
Class: |
H01G 009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2004 |
JP |
2004-058419(PAT.) |
Claims
What is claimed is:
1. An aluminum electrolytic capacitor produced by winding an anode
foil and a cathode foil via a separator impregnated with a driving
electrolyte solution, wherein: the driving electrolyte solution
contains a polar solvent, at least one electrolyte selected from
inorganic acids, organic acids, inorganic acid salts, and organic
acid salts, and a random copolymer of polyoxyethylene and
polyoxypropylene having a hydroxy group at one end and a hydrogen
group at the other end; and the separator is formed by overlaying a
cellulosic fiber-mixed paper, a cellulosic fiber paper, and a
cotton linter.
2. The aluminum electrolytic capacitor according to claim 1,
wherein the cellulosic fiber contains at least one fiber selected
from Manila jute, kraft, hemp, and esparto.
3. The aluminum electrolytic capacitor according to claim 1,
wherein the basis weight of the separator is in the range of 1 to
60 g/m.sup.2.
4. The aluminum electrolytic capacitor according to claim 1,
wherein the separator is previously subjected to paper-strength
reinforcement processing.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] The present invention relates to an aluminum electrolytic
capacitor for use in various electronic devices.
[0003] A configuration of the aluminum electrolytic capacitor
according to the present invention is shown in FIG. 1. The Figure
is a partial cross-sectional perspective view.
[0004] A capacitor element 19 in FIG. 1 is prepared by winding an
anode foil 11 and a cathode foil 12 via a separator 13, wherein the
anode foil 11 is obtained by etching a surface of an aluminum foil
to increase its effective surface area and subjecting the surface
to a chemical conversion treatment to form a dielectric oxide film
thereon, and the cathode foil 12 is obtained by etching a surface
of an aluminum foil. The aluminum electrolytic capacitor 19 can be
produced by connecting an anode lead terminal 15 and an cathode
lead terminal 16 respectively to the anode foil 11 and the cathode
foil 12, impregnating the capacitor element with a driving
electrolyte solution 14, placing the capacitor element 19 in a
metal case 18 such as aluminium case, and sealing the opening with
a sealing plate 17, for example, of rubber.
[0005] Many ion-conductive liquids, including those containing an
organic solvent such as ethylene glycol or .gamma.-butyllactone and
an electrolyte such as boric acid or ammonium borate, have been
used as the driving electrolyte solution 14. Alternatively,
non-aqueous electrolyte solutions containing one of dibasic acids
having a side-chain such as azelaic acid, butyloctanedicarboxylic
acid, and 5,6-decanedicarboxylic acid, or the salts thereof as the
electrolyte, which allows reduction of water in the driving
electrolyte solution 14, are said to be effective in suppressing
unintended release of the valves in the aluminum electrolytic
capacitor due to the increase in internal pressure by water even in
an environment of 100.degree. C. or more.
[0006] However, the nonaqueous driving electrolyte solutions 14
causes faster degradation of the electrolyte solution in an
esterification reaction at high temperature, and thus dibasic acids
having a side-chains such as butyloctanedicarboxylic acid,
5,6-decanedicarboxylic acid, and 1,7-octanedicarboxylic acid or the
salts thereof have been used in an electrolyte effective in
suppressing the esterification reaction.
[0007] Prior art references relevant to the present invention
include, for example, Jpn. Unexamined Patent Publication Nos.
05-226189 and 2001-313234.
[0008] Recently, for aluminum electrolytic capacitors for use in
anti-harmonic distortion circuits and vehicles, there exists a need
for a driving electrolyte solution 14 that is higher in electric
conductivity, superior in the spark voltage and the life at high
temperature, resistant to the breakdown of dielectric oxide films
on electrodes, superior in film-repairing ability for repairing the
defects once formed in the dielectric oxide film (hereinafter,
referred to as chemical self-restoring ability), and capable of
suppressing chemical reactions at high temperature.
[0009] However, when a dibasic acid having a side-chain or the salt
thereof is used as the electrolyte of a driving electrolyte
solution 14, the capacitor is likely to be less heat resistance at
high temperature, because the dibasic acid has a side-chain only in
the vicinity of the carboxyl group at one side. Also, the electric
conductivity of the electrolyte solution is likely to be lowering,
which may cause deteriorating the performance of the aluminum
electrolytic capacitor, because the carboxyl group of the
electrolyte reacts more with an alcohol such as ethylene glycol in
the esterification reaction when the capacitor is used for a
prolonged period.
[0010] In addition, the compounds above have an advantage that
increase in the amount and the molecular weight thereof leads to
increase in spark voltage, but on the contrary, become less soluble
in organic solvents especially at lower temperature, resulting in
precipitation. This restricts the range of the content or the
molecular weight of the compound. Accordingly, these compounds have
good solubility at lower temperature when they have a molecular
weight of 1,000 or less. However, as described above, reduction of
the molecular weight lead to an insufficient spark voltage and
possible short-circuit explosion during aging of the product. Thus,
there exist trade-off problems when these compounds are used for an
electrolyte.
[0011] Additionally, papers commonly used as separators 13 for
general aluminum electrolytic capacitors such as Manila paper,
kraft paper, and esparto paper have a high density. Reduction of
the density is likely to be less short-circuit resistance and to
lower tensile strength.
BRIEF SUMMARY OF INVENTION
[0012] The present invention is made to solve the aforementioned
problems, and an object thereof is to provide a high-ripple,
long-lasting driving electrolyte solution higher in electric
conductivity and superior in chemical self-restoring ability and
heat resistance at high temperature, and an aluminum electrolytic
capacitor using the same.
[0013] For the purpose of achieving the object above, the present
invention provides an aluminum electrolytic capacitor produced by
winding an anode foil and a cathode foil via a separator
impregnated with a driving electrolyte solution, wherein the
driving electrolyte solution contains a polar solvent, at least one
electrolyte selected from inorganic acids, organic acids, inorganic
acid salts, and organic acid salts, and a random copolymer of
polyoxyethylene and polyoxypropylene having a hydroxy group at one
end and a hydrogen group at the other end, and the separator is
formed by over laying a cellulosic fiber-mixed paper, a cellulosic
fiber paper, and a cotton linter.
[0014] The present invention provides an aluminum electrolytic
capacitor for use in anti-harmonic distortion circuits and vehicles
that is superior in the reliability and stability, for example,
withstanding voltage, heat resistance, ripple, life time, and
vibration resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a partial cross-sectional perspective view showing
the configuration of an aluminum electrolytic capacitor.
DETAILED DESCRIPTION OF INVENTION
[0016] The aluminum electrolytic capacitor in an embodiment of the
present invention has a configuration identical with that of the
conventional aluminum electrolytic capacitors described above and
for convenience, will be described with reference to FIG. 1. The
capacitor element 19 is formed by anode foil 11 and cathode foil 12
opposing to each other, which are wound together with intervening
separator 13. Anode foil 11 is an aluminum foil, the effective
surface area of foil 11 is enlarged through etching process and the
surface is provided with a dielectric oxide film formed through
anode oxidation process. It is provided with anode lead 15. Cathode
foil 12 is also formed of an etched aluminum foil, and provided
with cathode lead 16. The capacitor element 19 is placed inside an
aluminum case 18 after it is immersed in a driving electrolyte
solution 14, and the opening of the metal case 18 is sealed with a
sealing plate 17, to form an electrolyte capacitor.
[0017] The driving electrolyte solution 14 contains a polar
solvent; at least one electrolyte selected from inorganic acids,
organic acids, inorganic acid salts, and organic acid salts; and a
random copolymer of polyoxyethylene and polyoxypropylene having a
hydroxy group at one end and a hydrogen group at the other end.
[0018] Examples of the polar solvents include ethylene glycol,
propylene glycol, 1,4-butanediol, glycerine, polyoxyalkylene
polyols (polyethylene oxide, polypropylene oxide,
polyoxyethylene-oxypropylene glycol having a molecular weight of
200 or less, and the mixtures of two or more), amide solvents
(N-methylformamide, N,N-dimethylformamide, N-methylacetamide,
N-methylpyrrolidinone, etc.), alcohol solvents (methanol, ethanol,
etc.), ether solvents (methylal, 1,2-dimethoxyethane,
1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, etc.), nitrile
solvents (acetonitrile, 3-methoxypropionitrile, etc.), furan
solvents (2,5-dimethoxytetrahydrofur- an, etc.), sulfolane solvents
(sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, etc.),
carbonate solvents (propylene carbonate, ethylene carbonate,
diethyl carbonate, styrene carbonate, dimethyl carbonate, or methyl
ethyl carbonate, etc.), lactone solvents (.gamma.-butylolactone,
.gamma.-valerolactone, .delta.-valerolactone,
3-methyl-1,3-oxazolidine-2-one, 3-ethyl-1,3-oxazolidine-2-one,
etc.), imidazolidinone solvents (1,3-dimethyl-2-imidazolidinone,
etc.), and pyrrolidone solvents and the mixture of two or more, and
the like. Among these solvents, ethylene glycol, propylene glycol,
diethyleneglycol, water, lactone solvents, alcohol solvents,
carbonate solvents, ether solvents, nitrile solvents and furan
solvents are preferable. The amount of the polar solvent is
preferably 50 to 80% by mass with respect to the total amount of
the electrolyte solution.
[0019] The electorolyte contains at least one compound selected
from inorganic acids, organic acids, inorganic acid salts, and
organic acid salts. Favorable examples among them include boric
acid, phosphoric acid, benzoic acid, dibasic acids such as azelaic
acid, adipic acid, glutaric acid, phthalic acid, maleic acid,
5,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, and
1,6-decanedicarboxylic acid. These and salts thereof can be used as
the electrolyte. The salts above favorably used include ammonium
salts, amine salts, quaternary ammonium salts, amidine salts, and
the like.
[0020] The ammonium salt is, for example, a salt of an inorganic or
organic acid; examples of the amines for the amine salt include
primary amines (methylamine, ethylamine, propylamine, butylamine,
ethylenediamine, etc.), secondary amines (dimethylamine,
diethylamine, dipropylamine, methylethylamine, diphenylamine,
diethanolamine, etc.), and tertiary amines (trimethylamine,
triethylamine, tripropylamine, triphenyl amine, triethanolamine,
etc.); and examples the amidines for the amidine salt include
compounds having an alkyl-substituted amidine group, compounds
having a quaternarized alkyl-substituted amidine group, and
imidazole, benzimidazole, and alicyclic amidine compounds
quaternarized with an alkyl or arylalkyl group having 1 to 11
carbons.
[0021] Specific examples of the compounds having a quaternarized
alkyl-substituted amidine groups include
1-methyl-1,8-diazabicyclo[5,4,0]-
undecene-7,1-methyl-1,5-diazabicyclo[4,3,0]nonene-5,1,2,3-trimethylimidazo-
linium, 1,2,3,4-tetramethylimidazolinium,
1,2-dimethyl-3-ethyl-imidazolini- um,
1,3,4-trimethyl-2-ethylimidazolinium,
1,3-dimethyl-2-heptylimidazolini- um,
1,3-dimethyl-2-(3'-heptyl)imidazolinium,
1,3-dimethyl-2-dodecylimidazo- linium,
1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidinium,
1,3-dimethylimidazolinium, 1-methyl-3-ethyl-imidazolinium, and
1,3-dimethylbenzimidazolinium. The content of the electrolyte in
the electrolyte solution is preferably 10 to 30% by mass with
respect to the total amount of the electrolyte solution.
[0022] In addition, the random copolymer of polyoxyethylene and
polyoxypropylene having a hydroxy group at one end and a hydrogen
group at the other end has a structure represented by the following
General Formula (1).
HO--[(C.sub.2H.sub.4O).sub.n--(C.sub.3H.sub.6O).sub.m].sub.1--H
(1)
[0023] (n, m, and 1 each represent an integer.)
[0024] The copolymers having a hydroxy group at one end and a
hydrogen group at the other end have excellent solubility in polar
solvents and exhibit its advantageous effects more effectively.
[0025] Favorable repeating numbers of the monomer units of
oxyethylene and oxypropylene, n and m, in the random copolymer are
preferably 1 to 7 and 1 to 8 respectively. In addition, the number
of repeating unit 1 of the copolymer is preferably 1 to 10; and the
weight-average molecular weight is more preferably 1,000 to 3,000.
The weight-average molecular weight is a value calculated from the
hydroxyl value determined according to the method specified by JIS
K 1557.
[0026] In addition, the composition ratio of polyoxyethylene to
polyoxypropylene in the random copolymer is preferably 1/9 to 9/1
and more preferably 1/9 to 5/5 as the weight ratio of polyethylene
glycol to polypropylene glycol.
[0027] The content of the random copolymer in electrolyte solution
is preferably 1 to 5% by mass with respect to the total amount of
electrolyte solution.
[0028] The separator 13 has a structure formed by overlaying a
cellulosic fiber-mixed paper, a cellulosic fiber paper, and a
cotton linter. The method for overlaying these fibers is not
particularly limited, and, for example, the separator may be
prepared by overlaying the respective fiber one by one and
integrating the fibers by pressing the composite layer by means of
a roller or the like. Alternatively, the separator may be prepared
by first preparing double sheets of a cellulosic fiber-mixed paper
and a cellulosic fiber and then laying the double sheets over a
cotton linter. The cotton linter is preferably formed as the outer
layer when overlaid. Preferably, the cellulosic fiber-mixed paper,
the cellulosic fiber, and the cotton linter are overlaid in that
order. The separator is preferably placed in such a manner that the
cellulosic fiber-mixed paper and cotton linter face the electrode
foils. The cellulosic fiber according to the present invention
contains at least one fiber selected from Manila jute, kraft, hemp,
and esparto.
[0029] The separator according to the present invention has a dense
structure wherein the distance among the fibers is smaller, but
contains a great number of narrow through-holes. The structure
permits reduction of the resistance loss of capacitor without
decreasing the electric conductivity of the electrolyte solution
and also improvement of the short-circuit resistance. The thickness
of the separator in the present invention is preferably 40 to 80
.mu.m. The thickness of the cotton linter layer in the separator is
preferably 20 to 60 .mu.m. The thickness of the separator excluding
the cotton linter layer, i.e., the thickness of the cellulosic
fiber-mixed paper and the cellulosic fiber paper may be decided
arbitrarily, but the both papers may have the same thickness
substantively. Although other fibers may be used in the separator
according to the present invention in combination with the fibers
above, separators consisting essentially of the fibers described
above are preferable, and separators consisting of a cellulosic
fiber-mixed paper, a cellulosic fiber paper and a cotton linter are
particularly preferable.
[0030] The basis weight of the separator is preferably 1 to 60
g/m.sup.2. In contrast to conventional electrolyte solutions, which
often lead to short circuiting and thus was unable to provide
stabilized performance when a low-basis weight separator was used,
use of the driving electrolyte solution according to the present
invention enables physically securing the anode-cathode distance of
the capacitor and thus leads to improvement of the stability in
withstand voltage, allowing use of a low-basis weight separator in
medium- to high-voltage capacitors, which has been hitherto
difficult, and providing favorable capacitor performance. In
particular, use of the separator above enables drastic reduction of
the resistance due to the separator in the electrolytic capacitor,
and is thus effective in reducing the equivalent series resistance
(ESR) and the impedance of the capacitor.
[0031] A separator having a basis weight of less than 1 g/m.sup.2
does not have a sufficient short-circuit resistance, and a
separator of more than 60 g/m.sup.2 have an increased short-circuit
resistance but shows rather poor capacitor performance. The most
favorable range of the basis weight is 10 to 40 g/m.sup.2.
[0032] The basis weight is calculated as a product of the density
and the thickness of separator.
[0033] The separator 13 above may be subjected to a paper-strength
reinforcement processing for improvement in the tensile strength of
separator 13. The paper-strength reinforcement processing improves
the tensile strength as well as the short-circuit resistance of the
separator.
[0034] The paper-strength reinforcement processing may be carried
out by applying an aqueous solution of starch, vegetable gum,
carboxyalkylcellulose, polyoxyalkylene phthalate, or the like onto
the separator 13 or impregnating the separator with the
solution.
[0035] Any one of hitherto known aluminium foils may be used as the
electrode foil according to the present invention. The anode foil
may be produced by forming a dielectric oxide film by chemical
conversion on an aluminium foil surface having an effective surface
area expanded by etching. Alternatively, the cathode foil may be
prepared by etching an aluminium foil.
[0036] Hereinafter, the present embodiment will be described in
detail with reference to EXAMPLEs.
EXAMPLE 1
[0037] A capacitor element was prepared by winding an anode foil
and a cathode foil via a separator. The anode foil is prepared by
surface-roughening an aluminum foil by DC etching while making
tunnel-shaped pits vertically from the surface and forming a
dielectric oxide film (forming voltage 520 V) on the surface by
anodization. Cathode foil is an AC etched aluminium foil. The
separator has a structure formed by overlaying a cotton linter and
double sheets of a kraft-mixed paper and an esparto paper in the
order of a kraft-mixed paper, an esparto and a cotton linter (total
thickness: 50 .mu.m, kraft layer: 15 .mu.m, esparto layer: 15
.mu.m, cotton linter layer: 20 .mu.m, and basis weight: 25
g/m.sup.2).
[0038] The capacitor element above is then impregnated with each of
the electrolyte solutions. Each of compositions for driving
electrolyte solutions is shown in TABLE 1.
[0039] Each copolymer in the driving electrolyte solutions is a
random copolymer of polyoxyalkylene and polyoxypropylene having a
hydroxy group at one end and a hydrogen group at the other end, and
the weight ratio of polyethylene glycol to polypropylene glycol,
and the weight-average molecular weight of each copolymer is shown
in TABLE 2.
1TABLE 1 Composition of driving electrolyte Amount Electric
conductivity Spark voltage solution mass % (mS/cm) (V) Electrolyte
solution A Ethylene glycol 71.8 2.4 480 Ammonium benzoate 10
Ammonium 1,7-octandicarboxylate 16 Ammonium hypophosphite 0.2
Copolymer 1 2 Electrolyte solution B Ethylene glycol 72.5 2.2 460
p-Nitrobenzoic acid 10 Diammoium azelate 14 Monobutylphosphate 0.5
Copolymer 2 3 Electrolyte solution C Ethylene glycol 69.8 2.4 485
Ammonium benzoate 10 Diammoium azelate 13 Glycerine 5 Ammonium
hypophosphite 0.2 Copolymer 3 2 Electrolyte solution D Ethylene
glycol 56.5 2.7 495 p-Nitrobenzoic acid 10 Ammonium
1,7-octandicarboxylate 30 Ammonium hypophosphite 0.5 Copolymer 4 3
Electrolyte solution E Ethylene glycol 71.8 2.6 490 Ammonium
benzoate 10 Ammonium 1,7-octandicarboxylate 16 Ammonium
hypophosphite 0.2 Copolymer 5 2 Electrolyte solution F Ethylene
glycol 74.8 1.6 430 Ammonium benzoate 10 Diammoium azelate 10
Glycerine 5 Ammonium hypophosphite 0.2
[0040]
2 TABLE 2 Ratio of polyoxyethylene to polyoxypropylene Molecular
weight Copolymer 1 1:9 3,000 Copolymer 2 2:8 3,000 Copolymer 3 3:7
2,000 Copolymer 4 4:6 2,000 Copolymer 5 5:5 1,000
[0041] Subsequently, each of the capacitor elements above is placed
in a cylindrical aluminium metal case having a bottom plate and the
opening of the metal case was sealed with a cured-butyl rubber
sealant (butyl rubber polymer: 30 parts by mass, carbon: 20 parts
by mass, inorganic filler: 50 parts by mass, sealant hardness: 70
IRHD [international rubber hardness unit]) by a curling treatment,
to give an aluminum electrolytic capacitor.
EXAMPLE 2
[0042] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator formed by laying
double sheets of a Manila jute-mixed paper and a hemp paper over a
cotton linter (total thickness 50 .mu.m, Manila jute layer: 15
.mu.m, hemp layer: 15 .mu.m, cotton linter layer: 20 .mu.m, and
basis weight 25 g/m.sup.2) was used replacing the separator used in
EXAMPLE 1.
EXAMPLE 3
[0043] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator formed by laying
double sheets of a hemp-mixed paper and a kraft paper over a cotton
linter (total thickness: 50 .mu.m, hemp layer: 15 .mu.m, kraft
layer: 15 .mu.m, cotton linter layer: 20 .mu.m, and basis weight:
25 g/m.sup.2) was used replacing the separator used in EXAMPLE
1.
EXAMPLE 4
[0044] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator formed by laying
double sheets of a hemp-mixed paper and a kraft paper over a cotton
linter (total thickness: 50 .mu.m, hemp layer: 15 .mu.m, kraft
layer: 15 .mu.m, cotton linter layer: 20 .mu.m, and basis weight: 1
g/m.sup.2) was used replacing the separator used in EXAMPLE 1.
EXAMPLE 5
[0045] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator formed by laying
double sheets of a hemp-mixed paper and a kraft paper over a cotton
linter (total thickness: 50 .mu.m, hemp layer: 15 .mu.m, kraft
layer: 15 .mu.m, cotton linter layer: 20 .mu.m, and basis weight:
10 g/m.sup.2) was used replacing the separator used in EXAMPLE
1.
EXAMPLE 6
[0046] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator formed by laying
double sheets of a hemp-mixed paper and a kraft paper over a cotton
linter (total thickness: 50 .mu.m, hemp layer: 15 .mu.m, kraft
layer: 15 .mu.m, cotton linter layer: 20 .mu.m, and basis weight:
40 g/m.sup.2) was used replacing the separator used in EXAMPLE
1.
EXAMPLE 7
[0047] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator formed by laying
double sheets of a hemp-mixed paper and a kraft paper over a cotton
linter (total thickness: 50 .mu.m, hemp layer: 15 .mu.m, kraft
layer: 15 .mu.m, cotton linter layer: 20 .mu.m, and basis weight:
60 g/m.sup.2) was used replacing the separator used in EXAMPLE
1.
EXAMPLE 8
[0048] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator formed by laying
double sheets of a hemp-mixed paper and a kraft paper over a cotton
linter (total thickness: 50 .mu.m, hemp layer: 15 .mu.m, kraft
layer: 15 .mu.m, cotton linter layer: 20 .mu.m, and basis weight:
80 g/m.sup.2) was used replacing the separator used in EXAMPLE
1.
EXAMPLE 9
[0049] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator formed by laying
double sheets of a hemp-mixed paper and a kraft paper over a cotton
linter (total thickness: 50 .mu.m, hemp layer: 15 .mu.m, kraft
layer: 15 .mu.m, cotton linter layer: 20 .mu.m, and basis weight:
25 g/m.sup.2) that is further impregnated with an aqueous solution
of a carboxyalkylcellulose for improvement in paper strength was
used as the separator replacing the separator used in EXAMPLE
1.
EXAMPLE 10
[0050] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that the electrolyte solution B was
used replacing the driving electrolyte solution of EXAMPLE 1.
EXAMPLE 11
[0051] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that the electrolyte solution C was
used replacing the driving electrolyte solution of EXAMPLE 1.
EXAMPLE 12
[0052] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that the electrolyte solution D was
used replacing the driving electrolyte solution of EXAMPLE 1.
EXAMPLE 13
[0053] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that the electrolyte solution E was
used replacing the driving electrolyte solution of EXAMPLE 1.
COMPARATIVE EXAMPLE 1
[0054] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that the electrolyte solution F was
used replacing the driving electrolyte solution of EXAMPLE 1.
COMPARATIVE EXAMPLE 2
[0055] An aluminum electrolytic capacitor was prepared in a similar
manner to EXAMPLE 1, except that a separator of a mixed paper of
Manila jute and kraft (total thickness: 50 .mu.m, and basis weight:
25 g/m.sup.2) was used replacing the separator of EXAMPLE 1.
[0056] Twenty pieces of aluminum electrolytic capacitors of
EXAMPLEs 1 to 13 and COMPARATIVE EXAMPLEs 1 and 2 were prepared
respectively; the life tests thereof were performed; and the
results are summarized in TABLE 3. The rated outputs of the
aluminum electrolytic capacitors were respectively 47 .mu.F at 400
V, and ripple load tests were performed at a test temperature of
105.degree. C.
3 TABLE 3 After 2000 hr of ripple load at 105.degree. C. Initial
properties .DELTA.C tand LC ESR tand (%) LC (.mu.A) (%) (%) (.mu.A)
(.OMEGA.) EXAMPLE 1 4.3 24 -0.3 6.7 13 0.054 EXAMPLE 2 4.3 23 -0.5
6.6 12 0.030 EXAMPLE 3 4.1 25 -0.4 6.8 14 0.044 EXAMPLE 4 4.2 29
-0.8 7.9 21 0.001 EXAMPLE 5 4.8 25 -0.7 6.5 17 0.010 EXAMPLE 6 4.4
26 -0.5 6.6 14 0.089 EXAMPLE 7 4.7 25 -0.4 7.0 13 0.168 EXAMPLE 8
5.2 24 -0.5 7.7 14 0.192 EXAMPLE 9 4.5 24 -0.5 6.5 12 0.058 EXAMPLE
10 4.3 23 -0.4 6.6 13 0.056 EXAMPLE 11 4.4 25 -0.3 6.6 12 0.055
EXAMPLE 12 4.4 24 -0.4 6.7 14 0.058 EXAMPLE 13 4.5 24 -0.5 6.7 13
0.060 COMPARATIVE 10.2 56 -8.7 14.0 89 0.113 EXAMPLE 1 COMPARATIVE
Short circuiting during aging, 20/20 EXAMPLE 2
[0057] From the results in TABLE 1, it is apparent that the driving
electrolytes A to E containing a random copolymer of
polyoxyalkylene and polyoxypropylene having a hydroxy group at one
end and a hydrogen group at the other end have an electrical
conductivity and a spark voltage higher than those of the driving
electrolyte solution F not containing the random copolymer.
[0058] From the results in TABLE 3, it is also apparent that
combination of a driving electrolyte solution containing a random
copolymer of polyoxyalkylene and polyoxypropylene having a hydroxy
group at one end and a hydrogen group at the other end and a
separator having a structure formed by laying double sheets of a
cellulosic fiber-mixed paper, a cellulosic fiber paper over a
cotton linter, improves the properties such as change in capacity
(.DELTA.C), tan .delta., LC (Leak Current), and ESR after ripple
load test, compared to the cases of COMPARATIVE EXAMPLE 1 not using
a random copolymer and COMPARATIVE EXAMPLE 2 not using the cotton
linter.
[0059] As shown in EXAMPLEs 4 to 8, increase in the basis weight of
separator is accompanied with increase in tan .delta., LC, and ESR,
and thus the basis weight is preferably in the range of 10 to 40
g/m.sup.2.
[0060] As described above in detail, the aluminum electrolytic
capacitor according to the present invention is an aluminum
electrolytic capacitor produced by winding an anode foil and a
cathode foil via a separator impregnated with a driving electrolyte
solution, wherein the driving electrolyte solution contains a polar
solvent, at least one electrolyte selected from inorganic acids,
organic acids, inorganic acid salts, and organic acid salts, and a
random copolymer of polyoxyalkylene and polyoxypropylene having a
hydroxy group at one end and a hydrogen group at the other end, and
the separator is formed by overlaying a cellulosic fiber-mixed
paper, a cellulosic fiber paper, and a cotton linter. In the
present invention, the random copolymer of polyoxyalkylene and
polyoxypropylene having a hydroxy group at one end and a hydrogen
group at the other end is a copolymer of a polyoxyalkylene that is
superior in the solubility in polar solvents but have a drawback of
high crystallinity and a polyoxypropylene that is lower in the
solubility in polar solvents but lower in crystallinity,
compensating the drawbacks of each other; and thus, use of the
random copolymer overcomes the problem of precipitation at lower
temperature. Such a random copolymer also expands the range of
usable amount and molecular weight and raises the spark voltage and
improves the efficiency of chemical self-restoring ability forming
the chemical conversion film.
[0061] In addition, use of a random copolymer, which contains
monomers more randomly distributed, results in an orientation of
the copolymer at the air-liquid interface relatively sparser than
that of block copolymers. The structure raises the surface tension,
suppressing foaming of the electrolyte containing the random
copolymer during impregnation to the capacitor element, and
consequently the impregnation efficiency of a driving electrolyte
solution to the capacitor element is improved.
[0062] In addition, the cotton linter in the separator according to
the present invention has a shorter fiber having a fibril network
structure, although it is rater thicker. Thus, the fine fibers are
connected to each other at a numerous number of adhesion points.
Accordingly, the separator according to the invention has a surface
area greater than those of other separators when overlaying a
cellulosic fiber-mixed paper, a cellulosic fiber paper, and a
cotton linter. Thereby, a electrolyte-holding capacity of the
separator increases, the advantageous effects of the random
copolymer of polyoxyalkylene and polyoxypropylene are obtained more
efficiently, and the resistance loss of capacitor lowers. Thus, the
aluminum electrolytic capacitor of the present invention provides
superior properties in short-circuit resistance, withstand voltage,
heat resistance, ripple, life, and stability.
[0063] In the present invention described so far in details, all
description is provided here only to illustrate the present
invention by embodiments, and thus the present invention is not
limited thereto. It should be understood that numerous
modifications not exemplified here are also possible in the scope
of the invention.
[0064] This application is based on Japanese Patent Application No.
2004-58419 filed on Mar. 3, 2004, the contents of which are hereby
incorporated by references.
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